1. Field of the Invention
This invention relates to a method for forming an injection-molded piece of a given elaborate structure by injection-molding a metal or ceramic powder feed and processing the injection-molded piece into a precision component.
2. Prior Art
In recent years, precision components have been mass-produced by a molding technique, according to which a metal or ceramic powder feed is injection-molded into a piece having an elaborate, three-dimensional structure, sintering that injection-molded piece and finishing the thus sintered compact by highly accurate precision processings.
Applied to this molding technique is plastic injection-molding practically used so far in the art, in which metal or ceramic powders are heated and kneaded with an organic polymer plastics--usually referred to as a binder, a plasticizer, a surface active agent or diffuser to increase the mixing efficiency of the powder feed with the plastics and a fluidity improver, e.g., a wax, then granulated and finally injection-molded.
It is noted, however, the above-mentioned conventional technique has the following problems.
For the conventional injection-molding technique, a release agent must be coated on the mold used, as is the case with plastic molding. Although depending upon the type of release agent, however, the release agent used may have an adverse influence on the quality of post-molding sintered compacts or silver parts. Prior to being carried to the sintering step, the molded pieces or green parts must be cleared of the binder made up of plastics or, in a more proper term, degreased. Needed for degreasing are exclusive equipment, periods of time as long as about a few days and special technical means. If the binder, etc. are completely removed at the degreasing step, then the post-degreasing pieces or brown parts may deform or break down when carried into a sintering furnace; that is, a part of the binder, etc. must be left in them. However, the remaining binder, etc. may react with metal elements during sintering to form carbides, which may otherwise have an adverse influence on the quality of the silver parts.
As an alternative to the aforesaid injection-molding process, using sublimable substances for the binder, etc. has been proposed, but this involves a problem in connection with injection moldability. Freeze injection-molding has come to mind as well, but a freezing means must be taken along with a special means to remove moisture from the green parts without giving rise to their deformation. This freeze injection-molding is also subject to too much restriction to form three-dimensional green parts.
This invention has been accomplished with a view to providing a solution to the above-mentioned problems.